3,440 research outputs found
Abundant bacteria in the proximal and distal intestine of healthy Siberian sturgeons (Acipenser baerii)
The gut microbiota plays a key role in animal health, including immune and metabolic homeostasis. Despite the economic relevance of the sturgeon, studies addressing the gut microbiome of this species are scarce and have focused only on the hindgut. The objective of this work was to use Illumina metabarcoding technology to compare the bacterial microbiomes of two different intestinal locations, the proximal intestine (small intestine) and the distal intestine (hindgut containing the spiral valve), of healthy Siberian sturgeons (Acipenser baerii) reared on two different farms in Spain. Although a high degree of interindividual variability was observed, certain differences between the anatomical parts and between the geographical locations were clear. The results show that the sequences corresponding to the most abundant taxa were the basis for clustering according to anatomical region (proximal and distal intestine), whereas the less abundant taxa were the basis for clustering according to the geographical location of the fish farms. Finally, the results also indicate the existence of certain bacteria that are present in the intestinal tracts of all the fish analyzed in this study; this information may be useful in future studies aiming to establish differences based upon fish health or disease
Raman phonons as a probe of disorder, fluctuations and local structure in doped and undoped orthorhombic and rhombohedral manganites
We present a rationalization of the Raman spectra of orthorhombic and
rhombohedral, stoichiometric and doped, manganese perovskites. In particular we
study RMnO3 (R= La, Pr, Nd, Tb, Ho, Er, Y and Ca) and the different phases of
Ca or Sr doped RMnO3 compounds as well as cation deficient RMnO3. The spectra
of manganites can be understood as combinations of two kinds of spectra
corresponding to two structural configurations of MnO6 octahedra and
independently of the average structure obtained by diffraction techniques. The
main peaks of compounds with regular MnO6 octahedra, as CaMnO3, highly Ca doped
LaMnO3 or the metallic phases of Ca or Sr doped LaMnO3, are bending and tilt
MnO6 octahedra modes which correlate to R-O(1) bonds and Mn-O-Mn angles
respectively. In low and optimally doped manganites, the intensity and width of
the broad bands are related to the amplitude of the dynamic fluctuations
produced by polaron hopping in the paramagnetic insulating regime. The
activation energy, which is proportional to the polaron binding energy, is the
measure of this amplitude. This study permits to detect and confirm the
coexistence, in several compounds, of a paramagnetic matrix with lattice
polaron together with regions without dynamic or static octahedron distortions,
identical to the ferromagnetic metallic phase. We show that Raman spectroscopy
is an excellent tool to obtain information on the local structure of the
different micro or macro-phases present simultaneously in many manganites.Comment: Submitted to PR
Structure of ternary additive hard-sphere fluid mixtures
Monte Carlo simulations on the structural properties of ternary fluid
mixtures of additive hard spheres are reported. The results are compared with
those obtained from a recent analytical approximation [S. B. Yuste, A. Santos,
and M. Lopez de Haro, J. Chem. Phys. 108, 3683 (1998)] to the radial
distribution functions of hard-sphere mixtures and with the results derived
from the solution of the Ornstein-Zernike integral equation with both the
Martynov-Sarkisov and the Percus-Yevick closures. Very good agreement between
the results of the first two approaches and simulation is observed, with a
noticeable improvement over the Percus-Yevick predictions especially near
contact.Comment: 11 pages, including 8 figures; A minor change; accepted for
publication in PR
Growth and nanofabrication of all-perovskite superconducting/ferromagnetic/superconducting junctions
We fabricate and study experimentally all-perovskite-oxide superconductor/ferromagnetic insulator/superconductor (S/FI/S) tunnel junctions made out of the high-temperature cuprate superconductor YBa2Cu3O7−y (YBCO) and the colossal magnetoresistive manganite LaMnO3 (LMO) in the ferromagnetic insulator state. YBCO/LMO/YBCO heterostructures with different LMO thicknesses (5, 10, and 20 nm) are grown epitaxially via pulsed laser deposition. Nanoscale S/FI/S junctions with sizes down to 300 nm are made by three-dimensional nano-sculpturing with focused ion beam. Junctions with a thick (20 nm) LMO barrier exhibit a large negative magnetoresistance below TCurie∼160 K, typical for colossal magnetoresistive manganites, as well as a kink in the current-voltage characteristics at large bias (V∼1–2 Volts), attributed to Zener-type tunneling. However, they do not show a measurable Josephson current. On the contrary, junctions with the thinnest 5- nm LMO barrier exhibit a large supercurrent and no signs of magnetism. The latter may indicate the presence of pinholes due to thickness inhomogeneity and/or a ∼ 2 nm dead magnetic layer at the YBCO / LMO interface caused, e.g., by interdiffusion or strain. The junction with an intermediate 10-nm LMO barrier exhibited a desired S/FI/S junction behavior with significant negative magnetoresistance and signatures of a small Josephson current
Self-trapped Exciton and Franck-Condon Spectra Predicted in LaMnO
Because the ground state has cooperative Jahn-Teller order, electronic
excitations in LaMnO are predicted to self-trap by local rearrangement of
the lattice. The optical spectrum should show a Franck-Condon series, that is,
a Gaussian envelope of vibrational sidebands. Existing data are reinterpreted
in this way. The Raman spectrum is predicted to have strong multiphonon
features.Comment: 5 pages with two embedded postscript figure
The impact of genetic adaptation on chimpanzee subspecies differentiation
Published: November 25, 2019Chimpanzees, humans' closest relatives, are in danger of extinction. Aside from direct human impacts such as hunting and habitat destruction, a key threat is transmissible disease. As humans continue to encroach upon their habitats, which shrink in size and grow in density, the risk of inter-population and cross-species viral transmission increases, a point dramatically made in the reverse with the global HIV/AIDS pandemic. Inhabiting central Africa, the four subspecies of chimpanzees differ in demographic history and geographical range, and are likely differentially adapted to their particular local environments. To quantitatively explore s genetic adaptation, we investigated the genic enrichment for SNPs highly differentiated between chimpanzee subspecies. Previous analyses of such patterns in human populations exhibited limited evidence of adaptation. In contrast, chimpanzees show evidence of recent positive selection, with differences among subspecies. Specifically, we observe strong evidence of recent selection in eastern chimpanzees, with highly differentiated SNPs being uniquely enriched in genic sites in a way that is expected under recent adaptation but not under neutral evolution or background selection. These sites are enriched for genes involved in immune responses to pathogens, and for genes inferred to differentiate the immune response to infection by simian immunodeficiency virus (SIV) in natural vs. non-natural host species. Conversely, central chimpanzees exhibit an enrichment of signatures of positive selection only at cytokine receptors, due to selective sweeps in CCR3, CCR9 and CXCR6 -paralogs of CCR5 and CXCR4, the two major receptors utilized by HIV to enter human cells. Thus, our results suggest that positive selection has contributed to the genetic and phenotypic differentiation of chimpanzee subspecies, and that viruses likely play a predominate role in this differentiation, with SIV being a likely selective agent. Interestingly, our results suggest that SIV has elicited distinctive adaptive responses in these two chimpanzee subspecies.Joshua M. Schmidt, Marc de Manuel, Tomas Marques-Bonet, Sergi Castellano, Aida M. André
Non-Extremal D-instantons and the AdS/CFT Correspondence
We investigate non-extremal D-instantons in an asymptotically background and the role they play in the correspondence.
We find that the holographic dual operators of non-extremal D-instanton
configurations do not correspond to self-dual Yang-Mills instantons, and we
compute explicitly the deviation from self-duality. Furthermore, a class of
non-extremal D-instantons yield Euclidean axionic wormhole solutions with two
asymptotic boundaries. After Wick rotating, this provides a playground for
investigating holography in the presence of cosmological singularities in a
closed universe.Comment: 30 pages, 3 figure
Lifetimes of image-potential states on copper surfaces
The lifetime of image states, which represent a key quantity to probe the
coupling of surface electronic states with the solid substrate, have been
recently determined for quantum numbers on Cu(100) by using
time-resolved two-photon photoemission in combination with the coherent
excitation of several states (U. H\"ofer et al, Science 277, 1480 (1997)). We
here report theoretical investigations of the lifetime of image states on
copper surfaces. We evaluate the lifetimes from the knowledge of the
self-energy of the excited quasiparticle, which we compute within the GW
approximation of many-body theory. Single-particle wave functions are obtained
by solving the Schr\"odinger equation with a realistic one-dimensional model
potential, and the screened interaction is evaluated in the random-phase
approximation (RPA). Our results are in good agreement with the experimentally
determined decay times.Comment: 4 pages, 1 figure, to appear in Phys. Rev. Let
Ages and Metallicities of Star Clusters and Surrounding Fields in the Outer Disk of the Large Magellanic Cloud
We present Washington system C,T_1 CMDs of 13 star clusters and their
surrounding fields which lie in the outer parts of the LMC disk. Ages are
determined by means of the magnitude difference between the giant branch clump
and the turnoff, while metallicities are derived from the location of the giant
and subgiant branches as compared to fiducial star clusters. We find that in
most cases the stellar population of each star cluster is quite similar to that
of the field where it is embedded. Three particular fields present remarkable
properties: (i) The so far unique cluster ESO121-SC03 at ~9 Gyr has a
surrounding field which shares the same properties. (ii) The field surrounding
the far eastern intermediate age cluster OHSC37 is noteworthy in the sense that
we do not detect any evidence of LMC stars. (iii) The fields of SL388 and SL509
present CMDs with a secondary clump ~0.45 mag fainter than the dominant
intermediate age clump, suggesting a stellar population component located
behind the LMC disk at a distance comparable to that of the SMC. The mean
metallicity derived for the intermediate age outer disk clusters is
=-0.7 and for their surrounding fields =-0.6. These values are
significantly lower than found by Olszewski et al. (1991, AJ, 101, 515) for a
sample of clusters of similar age, but are in good agreement with several
recent studies. A few clusters stand out in the age--metallicity relation in
the sense that they are intermediate age clusters at relatively low metallicity
([Fe/H]~-1).Comment: LaTeX, to be published in July, 1998 Astronomical Journa
Limits to the muon flux from WIMP annihilation in the center of the Earth with the AMANDA detector
A search for nearly vertical up-going muon-neutrinos from neutralino
annihilations in the center of the Earth has been performed with the AMANDA-B10
neutrino detector. The data sample collected in 130.1 days of live-time in
1997, ~10^9 events, has been analyzed for this search. No excess over the
expected atmospheric neutrino background is oberved. An upper limit at 90%
confidence level on the annihilation rate of neutralinos in the center of the
Earth is obtained as a function of the neutralino mass in the range 100
GeV-5000 GeV, as well as the corresponding muon flux limit.Comment: 14 pages, 11 figures. Version accepted for publication in Physical
Review
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